The petrology of a melilitolite, carbonatite, melteigite and syenite ring dike system, Gardiner Complex, East Greenland

The Tertiary Gardiner complex in East Greenland comprises ultramafic cumulates cut by dikes, ring dikes and cone sheets. One major ring dike is of melilite-rick rocks (melilitolites), and shows phase layering and cryptic layering with respect to melilite, perovskite and phologopite. The vertical variation in the assemblages through the ring dike is consistent with established fractionation trends in undersaturated melilite-bearing experimental systems. Related veins and dikes are: a) undersaturated rocks of the melteigite-ijolite-urtite/nepheline syenite suite, b) melanite-calcite veins and søvite dikes and sheets and c) coarse-grained magnetite-phlogopite-diopside-calcite pegmatites and dolomite rocks. It is proposed that a CO2-bearing Ln-normative nephelinite liquid is parential to both melilitolites and related veins through a combination of fractional crystallization, liquid immiscibility and CO2-metasomatism of dunite country rocks. Unlike other localities where melilitolites are attributed to metasomatic processes, the Gardiner melilitolites are magmatic.